Although any period of ten years is a decade,[1][2] a convenient and frequently referenced interval is based on the tens digit of the calendar year, as in using 1960s to represent the decade from 1960 to 1969...Some writers[5] like to point out that since the common calendar starts from the year 1, its first full decade contained the years from 1 to 10, the second decade from 11 to 20, and so on. The interval from the year 2001 to 2010 could thus be called the 201st decade, using ordinal numbers. However, contrary to practices in referencing centuries, ordinal references to decades are quite uncommon.

Although any period of ten years is a decade,[1][2] a convenient and frequently referenced interval is based on the tens digit of the calendar year, as in using 1960s to represent the decade from 1960 to 1969...Some writers[5] like to point out that since the common calendar starts from the year 1, its first full decade contained the years from 1 to 10, the second decade from 11 to 20, and so on. The interval from the year 2001 to 2010 could thus be called the 201st decade, using ordinal numbers. However, contrary to practices in referencing centuries, ordinal references to decades are quite uncommon.